Atomic hopping induced dynamic disorder phonon scattering and suppressed thermal transport in Cu4TiSe4

Abstract

<p>Thermal transport in electrical insulators is governed by phonons, which are strongly influenced by atomic dynamics. Fast atomic diffusion enhances phonon scattering in superionic materials but causes uncompromising convectional heat flux, leading to an increase in lattice thermal conductivity (<em>κ</em>_L) with temperature. Here, we performed molecular dynamics simulations with machine learning potential, uncovering the hopping behavior of Cu2 atoms in Cu₄TiSe₄ between adjacent sites 1<em>a</em> and 4<em>e</em>, which exhibit much lower diffusion coefficients compared to those in typical superionic materials. This hopping behavior induces additional dynamic disorder scattering, while its contribution to convectional heat flux is negligible, as evidenced by the decreased <em>κ</em>_L with rising temperature in both experiments and calculations. The dynamic disorder is sufficiently strong to inhibit the propagation of Cu2-dominated short-wavelength phonons near the Brillouin zone boundary and greatly enhances the scattering of long-wavelength acoustic phonons in Cu₄TiSe₄. Further analysis of mode-projected phonon linewidths reveals that the dynamic disorder significantly enhances phonon scatterings and plays a dominant role in thermal transport, elucidating the mechanism behind the remarkably low <em>κ</em>_L of Cu₄TiSe₄. This work provides insights into the correlation between atomic dynamics and phonon scattering, offering potential avenues for the discovery and phonon engineering of ultralow-<em>κ</em>_L materials.<br></p>